How to reconcile the Paris Agreement's target to deliver a temperature rise 'well under 2C', with its wholly inadequate mechanisms? Easy, writes Myles Allen: Make fossil fuel producers 'take back' their carbon so as to fit within a global carbon budget. And for fossil fuel producers in the rich world, that means there is no time to lose - specially to meet a 1.5C target.

We are already at 1C, and stabilising temperatures requires net zero CO2 emissions. So to stabilise at 2C, we need to reduce emissions by 10% of today's value for every tenth of a degree of warming. And for 1.5 degrees, it's 20% per tenth of a degree.

I wonder how many of the delegates in Paris realise that they have just created the mother of all 'take-back schemes'.

As a consumer, you may have already come across this sort of deal: if you don't want to dispose of the packaging of your new sofa, you can take it back to IKEA and it's their problem.

In many places, you can even take back the sofa itself when your kids have wrecked it.

For the Paris climate deal to succeed something similar will have to happen, where companies that rely on fossil fuels will be obliged to 'take back' their emissions.

The agreement reaffirms a commitment to stabilising temperature rises well below 2C, and even retains the option of limiting warming to 1.5C if possible. But it also confirms national targets that do little more than stabilise global emissions between now and 2030.

Given those emissions, sticking to within 2C will require us to take lots of carbon out of the atmosphere and store it in the ground. The parties to the agreement are, in effect, saying "we're going to sell this stuff, and we're going to dispose of it later."

How do I know? Well, peak warming is overwhelmingly determined by cumulative carbon dioxide emissions. To stabilise temperatures at any level, be it 1.5C, 2C or even 3C, net carbon dioxide emissions must be reduced to zero. Most governments, environmental groups and business leaders now understand this.

And it is acknowledged, albeit implicitly, in Article 4 of the Paris agreement, which calls for greenhouse emissions to be 'balanced' by carbon sinks some time after mid-century. But we're unlikely to hit 'net zero' emissions before temperatures reach 2C, and even less likely before they reach 1.5C.

Warming is currently at about 1C and rising by 0.1C every five to ten years. We could slow the warming by reducing emissions, of course. But if we fail to reduce at the required rate - and the inadequate emissions targets indicate this is the intention - then we will be left with no option but to scrub the excess CO2 back out of the atmosphere in future.

Who should take back the CO2? The fossil fuel producers

That is why the deal is like a gigantic take-back scheme. The proof lies in what is not said in the Paris agreement. There is no explicit mention of a global carbon budget for instance, which adds up total emissions since the industrial revolution.

That is despite the fact that all governments have acknowledged, through the Intergovernmental Panel on Climate Change, the reality that stabilising temperatures requires a limit on cumulative CO2 emissions. Certain countries simply cannot accept the suggestion that they may be obliged to leave some of their prized fossil carbon reserves underground.

And why should they? We do not need, and nor have we any right, to ban India from using its coal. We simply need to ensure that, by the time we reach 2C, or 1.5C if that is what is eventually deemed safe, any company that sells fossil fuels, or any carbon-intensive product like conventional cement, is obliged to take back an equivalent amount of CO2 and dispose of it safely to ensure it doesn't end up in the atmosphere.

Right now, that means re-injection underground: forests can't be relied on over geological timescales (they might burn down, or even die out and re-release their carbon due to climate change itself). But there are plenty of other creative ideas for carbon dioxide disposal: someone just needs the incentive to do it.

And who better than the owners of the fossil fuel assets at the heart of the problem? Logically, the cost of CO2 disposal should be borne by the seller of fossil carbon.

If it is paid for out of general taxation, no one will have any incentive to minimise the carbon content in the products they sell or buy, nor will companies have an incentive to minimise the cost of disposal. And relying on taxpayers to pay for disposal makes it vulnerable every time the purse strings are tightened.

It's the only way to stabilise the climate

The idea of a 'CO2 take-back' scheme was suggested by Nick Robins, a UN sustainability adviser, at a recent event in Paris. It may have been meant as a whimsical aside, but it really is the only feasible way of stabilising the climate. The alternative - a global ban on fossil fuel extraction and use - is neither ethical nor enforceable.

Enthusiasts for renewable energy would like us to believe they can make it cheaper than coal, so a global ban would be unnecessary. But there will still be cement, jet fuel, fertiliser - the list is endless.

The idea that we will develop a cheaper substitute for every single application of fossil carbon, everywhere in the world, before temperatures reach 2C, is pure fantasy. As Ottmar Edenhofer, one of the world's leading climate economists, put it: "As a Catholic, I believe in miracles, but I do not rely on them."

Of course, if we include the costs of take-back, then high-carbon products will become more expensive, which is all good for renewables. But unlike new taxes, take-back schemes are generally popular despite industry's dire warnings about increased costs.

People understand that the main beneficiary of fancy packaging is the company selling the product. And even at today's prices, the main beneficiaries of our continued use of fossil fuels is not the long-suffering consumer, nor even the firm with its logo on the pump, but those who hoover up the royalties, taxes and rents as fossil fuels come out of the ground.

For 2C / 1.5C, a 10% / 20% cut for every 0.1C of warming. Starting now

Earlier this year, I suggested that something like a CO2 take-back scheme (although not with nearly such a catchy name) should be considered in the UK energy bill, and was promptly taken out for a coffee by a well-spoken industry lobbyist to tell me what a bad idea it was. To my mind, that rather suggested that I was onto something.

'Mandatory sequestration' hasn't really caught on in the environmental movement, partly I'm sure because it is a bit of a mouthful for any campaigner.

But stack up the net zero emissions point against the inadequate national targets, and you soon realise that all those shouting "1.5 to stay alive" in Paris (and there were plenty) were actually advocating a crash programme of CO2 disposal.

So when should we start? Indications are that if we allow emissions to keep on growing at 2% per annum as they have been, the world's entire estimated 'carbon budget' of 840GtC that's considered likely to deliver an under 2C temperature rise will have been reached in 20 years time, in 2035. To deliver 1.5C, that means putting even less carbon out there.

So here's a plan of action. We are already at 1C, and stabilising temperatures requires net zero CO2 emissions. So to stabilise at 2C, we need to reduce emissions, on average, by 10% of today's value for every tenth of a degree of warming from now on. And to stabilise at 1.5 degrees, we need to reduce, on average, by 20% per tenth of a degree of warming.

It really is that simple - and right now, the world is warming by a tenth of a degree every 5-10 years. There is no time to lose.

#takebackCO2 - start tweeting it now!

Myles Allen is Professor of Geosystem Science, Leader of ECI Climate Research Programme, University of Oxford.